(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Text Book Of Mechanical Engineering"

Various Methods of Moulding.

5

:ings, ribbed

;as from the

.d and loamj
easures, that
sand should
ogether with
poses. The
>f silica in its
mch as 93 or
:r substances.
) much when
, it should at
.ssage of airr
[ entering it.
sous*) with a
It is ground
, horse dung,
rosity.

Dck sand and
i, for the use
blast-furnace
Derfectly dry.
hods: Green

In green and dry sand moulding, patterns are generally used;
but in loam  moulding, which is only employed for objects of
regular form, the mould is struck out by means of a template, \
and built up by the moulder himself

* Green Sand is the geological name of a sand of very fine
texture. It appears black in the foundry because it is mixed with
a proportion of coal and charcoal dust; it is damped each time
that it is used. This is the most general method of moulding,
with castings not likely to warp too much by the more rapid
cooling. (See Appendix //.,/. 779.)

v Dry Sand is a mixture of old loam with an addition of
rock sand. It is so called because, after the pattern is moulded,
the sand is dried by means of fires hung in pans or trays over
the moulds. It is firmer and more suitable for the support of
long castings, such as pipes, columns, and large fly-wheels than
green sand is, and will produce finer castings, with less fear
of pieces of sand being torn away by the
flow of the metal. If pipes are moulded
in green sand, the tendency is to uneven
thickness in the castings, through sagging
of the sand.

 Loam Moulding, as we have said,
does not require a pattern, the mould
being struck in the pasty loam (the latter
being mixed with water) by means of a
rotating or sliding template, called a
* striking-board. Thus the core of a large
cylinder, is built up in brickwork, and then
covered with a layer of loam, which is
smoothed by a rotating striking - board

(see Fig. 3), much as a plasterer would work the cornice of a
house ceiling. Cubical moulds, such as those for condensers,
may also be worked in loam.

The simplest moulding done in green sand is called Open
Sand Moulding, and consists in laying the pattern in the sand
on the foundry floor, withdrawing, and then pouring in the metal,
a cover not being used. This is the method employed for such
common objects as moulding boxes (see Fig. 4).

wank.